Tanks are commonly used for storing fluids. Environmental damage may occur if a fluid storage tank leaks. Obviously the nature and extent of damage caused by leakage from a tank will depend on the nature of the fluid in the tank and the amount of leakage. Where tanks are above-ground, they can be monitored by visual inspection. However, in many circumstances fluid storage tanks are located underground. Underground fuel storage tanks are used at filling stations for the storage of petroleum products. Leakage of petroleum products from an underground storage tank might go unnoticed for many months, during which time water courses may be polluted, and soil may be contaminated. Furthermore, people and buildings in the vicinity may be endangered by the presence of highly flammable fuels in the ground.
Historically, underground fuel storage tanks were fashioned from a single skin of mild steel. Corrosion of such tanks was not a problem whilst petrol fuel contained lead, the lead acting as a corrosion inhibitor. However, in most countries lead is no longer present in petrol fuel. The resulting petrol fuel is corrosive of steel, and there have been a number of incidences of such tanks leaking fuel into the ground with consequent damaging effects. There is therefore a move to line underground fuel storage tanks with linings not susceptible to corrosion by the fuel destined to be stored in the tank.
If a double skinned tank contains an air gap between the outer tank wall and the interior lining, leakage from the tank can be monitored by various leak monitoring devices. One such leak monitoring device monitors a vacuum in the air gap. A change in pressure indicates an integrity failure in the inner lining or outer hull.
The replacement of an underground tank is a time consuming and expensive process, since in the case of a filling station, the cost of physically removing the tank from the ground is itself high, but more importantly whilst the tank is being replaced the fuel station must be closed, resulting in loss of revenue for the period of closure, and possible long-term loss of business due to customers going to other filling stations during the period of closure.
Re-lining existing underground tanks provides at least three benefits. First, the lining is selected so as not to be corrodible by the fuel. Second, if there is an interstitial space this space can be monitored to establish whether there is any leakage of fuel from the tank, and third, lining a tank can be accomplished more quickly than replacement of a tank.
The publication WO 00/32394 describes a method of lining a fuel storage tank in which a keying means is applied to the surface of a tank. A corrosion barrier is then applied to the keying means. An interstitial grid is then applied to the tank and pliable glass reinforced plastics material is laid onto the grid. The glass reinforced plastics material is then exposed to ultra violet rays to cure the material and form a hardened inner liner shell for the tank.
To line a tank following the method described in WO 00/32394 requires a team of men working for thirty to forty five days, with one man of the team working in the tank at any one time. Due to the toxic nature of the gases given off by the resins used in the laying up of the pliable glass reinforced plastics material onto the grid, and the ability of those gases to pass through the skin and into the bloodstream of humans, the length of time a worker may spend in the tank is severely limited, and special protective clothing must be worn and breathing apparatus used. Whilst in the tank the workers wear clothing that is impervious to the gases given off by the resins used in the laying up of the glass reinforced plastics material. However, the protective clothing available is only impervious to these gases for a limited period of time, after which the worker must come out of the tank, dispose of the protective clothing and be de-contaminated. The risk of hospitalisation resulting from exposure to noxious gases during the laying up the glass reinforced plastics material is significant.
Another apparatus and method of lining a tank is disclosed in GB 2413587. This apparatus requires the tank to be lined with a material having protrusions on one side, the free ends of which face the inner wall of the tank and are glued thereto. Seams between adjoining sections of material may be joined together, or a second layer of material may cover the first, with adjoining sections thereof being attached to each other to form a sealed lining. Whilst this re-lining apparatus and method provides for effective sealing and reduces the problems associated with working in a confined environment when exposed to noxious gases, performance of the method of re-lining is time consuming.
Another apparatus and method of lining a tank is disclosed in PCT/GB2006/050069. In this apparatus and method the tank is lined with a single layer of fluid impervious plastics material. An interstitial space exists between opposing faces of said wall and said plastics sheet which is monitored by a vacuum. This apparatus and method uses fewer and less costly materials than the method of GB 2413587, and the time required to perform the method is reduced. Nevertheless an apparatus and method yet more efficient would be desirable.
The apparatus and method of GB 0511243.8 (not published) provides an alternative apparatus and method for lining a tank which is less time consuming to install than those of GB 2413587 and GB 0522817.6 (not published). However, this particular apparatus is not suitable for use with liquids having high penetrability such as petrol.
Another apparatus and method of lining a tank is described in GB 0608233.3 (not published). This particular apparatus and method uses double sided sticky tape to attach the lining to the inner surface of the tank hull. One problem associated with this lining apparatus and method is that the weight of liquid in the tank may depress the fluid impervious layer such that the interstitial space is compromised.
It would therefore be desirable to provide an improved apparatus and method.